Altec catalogue 1980
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Page 2
LOUDSPEAKER ENCLOSURES
THEIR DESIGN AND USE
INTRODUCTION
Altec has created this publication to pro-
vrde a source of data trom which audio
enthusiasts can design and construct
enclosures ol predictable and satisfac-
tory performance when used with Altec
loudspeakers. For simplicity. at Altec. we
think of the loudspeaker being the trans:
ducer. or raw frame, and a speaker being
the completed system-including enclo-
sure. It is not intended to contain intor-
matron for all types oi audio systems.
such as theatrical and sound reinforce-
ment systems or enclosure design prlnr
ciples not used in Altec tactory»built
systems. The concepts are presented
from a practical standpoint. in order that
the beginner may better understand the
principles involved to design and build
his own enclosure. To make music. not
textbooks
Function of an Enclosure
The purpose oi the loudspeaker enclo-
sure is to provide proper coupling
between the loudspeaker transducer and
the air into which the loudspeaker plays.
The requirement tor proper coupling is
due to the piston-like action of the loud»
speaker diaphragm when activated by a
signal. It a loudspeaker transducer were
ireely suspended in the air, and then
required to reproduce bass trequencies.
little uselul response would be obtained,
The reason this occurs is the actual cone/
diaphragm motion. which sets up a con-
dition called "Phase Cancellation."
l A.
The Loudspeaker Motion
The loudspeaker is essentially an air
pump, converting electrical source
energy into mechanical impulses. which
are translerred to the air adjacent to the
cone. To generate a desired audible tone.
the loudspeaker cone must not only
vibrate at the proper frequency, but must
also set into motion a sutlicient volume
oi air to create the Vibration we perceive
as sound. Sound waves are generated
equally on both sides oi the cone. but
are opposite in their phase relationship.
When the cone moves torward, the air
at the tront ol the diaphragm is com-
pressed. while the air at the rear ol the
cone is rarelled. The reproduction of an
audio signal requires that the loud"
speaker diaphragm must move through
both a lorward and a rear directed motion
With each hertz 0! signal. The opposite
condition of compression and rarelaction
is then created on the rear directed
motion of the diaphragm. The eltect is
l
illustrated in Figures 1A and 13. Thus.
each halt»hertz ol signal is created t80
degrees out-of-phase with the next
successive half-hertz signal; this as the
loudspeaker diaphragm Completes its
reproduction ol each lu||~hertz Signal
Such cancellations are detrimental to
performance. and prevent the loud-
speaker lrom transmitting the cone
energy into usable response in the air oi
the listening area.
Figure 1
Page 2
LOUDSPEAKER ENCLOSURES
THEIR DESIGN AND USE
INTRODUCTION
Altec has created this publication to pro-
vrde a source of data trom which audio
enthusiasts can design and construct
enclosures ol predictable and satisfac-
tory performance when used with Altec
loudspeakers. For simplicity. at Altec. we
think of the loudspeaker being the trans:
ducer. or raw frame, and a speaker being
the completed system-including enclo-
sure. It is not intended to contain intor-
matron for all types oi audio systems.
such as theatrical and sound reinforce-
ment systems or enclosure design prlnr
ciples not used in Altec tactory»built
systems. The concepts are presented
from a practical standpoint. in order that
the beginner may better understand the
principles involved to design and build
his own enclosure. To make music. not
textbooks
Function of an Enclosure
The purpose oi the loudspeaker enclo-
sure is to provide proper coupling
between the loudspeaker transducer and
the air into which the loudspeaker plays.
The requirement tor proper coupling is
due to the piston-like action of the loud»
speaker diaphragm when activated by a
signal. It a loudspeaker transducer were
ireely suspended in the air, and then
required to reproduce bass trequencies.
little uselul response would be obtained,
The reason this occurs is the actual cone/
diaphragm motion. which sets up a con-
dition called "Phase Cancellation."
l A.
The Loudspeaker Motion
The loudspeaker is essentially an air
pump, converting electrical source
energy into mechanical impulses. which
are translerred to the air adjacent to the
cone. To generate a desired audible tone.
the loudspeaker cone must not only
vibrate at the proper frequency, but must
also set into motion a sutlicient volume
oi air to create the Vibration we perceive
as sound. Sound waves are generated
equally on both sides oi the cone. but
are opposite in their phase relationship.
When the cone moves torward, the air
at the tront ol the diaphragm is com-
pressed. while the air at the rear ol the
cone is rarelled. The reproduction of an
audio signal requires that the loud"
speaker diaphragm must move through
both a lorward and a rear directed motion
With each hertz 0! signal. The opposite
condition of compression and rarelaction
is then created on the rear directed
motion of the diaphragm. The eltect is
l
illustrated in Figures 1A and 13. Thus.
each halt»hertz ol signal is created t80
degrees out-of-phase with the next
successive half-hertz signal; this as the
loudspeaker diaphragm Completes its
reproduction ol each lu||~hertz Signal
Such cancellations are detrimental to
performance. and prevent the loud-
speaker lrom transmitting the cone
energy into usable response in the air oi
the listening area.
Figure 1